In many places in the world, rats are regarded as a vile nuisance and a menace to society. But the truth is that scientists, researchers and even police and health care workers are discovering how useful our ancient foe, the common brown rat, can actually be.

Aaron Blaisdell, a professor of comparative psychology at the University of California in Los Angeles, has found that rats are a lot smarter than we give them credit for.

“They’ve always been really good in basic learning experiments, like Pavlovian conditioning, Skinnerian conditioning and things like that,” Blaisdell says. “But we increasingly understand that some of the core elements of what we think of as human-like cognition are present in rats”.

Monique Hammerslag, an inspector with the Dutch National Police, is training rats to discriminate between certain brands of cigarettes and counterfeits — and they are already quite good at it.

Rats are great for this kind of work, Blaisdell says, because they’re “very olfactory driven. … Rodents in general have a really good sense of smell, which makes them very useful for detecting things based on the chemical signature that’s unique to that substance,” he explains.

Training them is quite easy. They are very intelligent, Blaisdell says, not just in learning, but also in reasoning processes. Beyond that, they live in large groups and so they are very social.

“They have a lot of the social mechanisms of behavior that are present in, for example, primates or pack hunting dogs and wolves,” Blaisdell says. “So, they actually form a good bond with a human. If they are raised in captivity or domesticated, they will come to you if you call them. … I kind of think of them as cuddly cats or puppy dogs.”

Hammerslag says rats will never replace dogs in police work, but they can supplement them. “Because a dog is a hunter, you can take a dog to new places and they go search for you. They don’t mind if they go to a place they’ve never been before,” she explains. “A rat will often freeze in a new place, so that’s not very practical for police work. But what rats can do very well is smell samples, which is a bit of boring job and not very interesting for dogs.”

Workers in Africa are using rats’ olfactory abilities for a different kind of task: clearing land-mines. These so-called “giant” Gambian pouched rats are a different species from the common brown rat, probably more closely related to the hamster, Hammerslag says.

“My rat is the Rattus norvegicus, the brown rat, and the other one is the Cricetomys gambianus,” she explains. “It’s a different species. It’s also much bigger.”

The giant rats have another advantage: They store their food, which is payment for their work, in their cheeks and put off eating until their task is completed. “This is very practical, because when you train them, they don’t get full,” Hammerslag says. “Whereas my rats immediately eat their reward, the pouched rats just store it and they start eating after the work.”

Like dogs, rats can be trained to understand vocal cues, though it’s not clear to what extent. “Based on my understanding, rats can learn lots of associations between other stimulae, such as odor and visual cues, so I imagine they can learn dozens [of vocal cues], at least,” Blaisdell says.

Hammerslag concurs. She names her rats after people who helped her in her first projects with rats, and they respond to their names. “When I call, for example, “Ed,” Ed comes out,” she says.

HammersIag feels sentimental about her rats — an unfamiliar feeling to many of us. “I really love the guys and I feel attached to them,” she says. “They are very, very nice animals, very friendly [and] they never bite. They never do bad things.”

She has no pet rats at the moment, but when this group retires, she will likely take them home. Unfortunately, she says, rats don’t live very long, typically only two to three years. “That’s the hard thing about training rats and working with them,” Hammerlsag says. “You have to say goodbye rather fast.”